Many biochemical operations can be facilitated by differentially labeling two samples that differ in only one parameter, performing biochemical separations on the mixture and afterward determining the amount of each label in each separated spot. Such measurements are easiest to perform and most accurate when both isotopes are measured concurrently rather than sequentially. Recent work has shown the utility of this approach to determine proteins that are more or less abundant in cancerous tissue compared to normal. We plan to develop a Dual MPD Imager to measure the planar distribution of two isotopes of iodine (125-I and 131-I) in samples such as 2D gels, TLC plates, protein chips, etc. The dual imager will separately measure the amount of each isotope in a single scan. We expect to have less than 1% cross talk between the two labels and better than 0.5 mm spatial resolution. Preliminary results show an excellent separation of signals from the two isotopes.